The present invention is concerned with a floating-frame spot-type disc brake for high-torque automotive vehicles designed for high performance.
Automotive vehicles designed for high driving speeds require increasingly efficient brakes. High-torque brakes, among other things, require large brake disc diameters. Conversely, the diameters of the vehicle wheels is set by other factors not allowing an increase in wheel diameter. These two requirements severely restrict the assembly space available for the brake between the outer brake disc edge and the wheel rim. Normally the brake caliper of a disc brake encloses the outer edge of the brake disc, with the radial dimensions of a bridge of the brake caliper located in the aforementioned assembly space limiting the maximum brake disc diameter. The caliper bridge, conversely, is required to have substantial strength as it transmits the tensile forces required for braking.
In a prior-art solution of the type as described in DE-OS 35 08 039, the brake disc has been replaced by an annular disc, the radial inner edge of which is enclosed by the brake caliper (internally enclosing disc brake). The radially outer edge of the annular disc substantially extends to the wheel rim, with the maximum possible diameter being attained. However, this high-torque brake is disadvantageous in that the manufacture and assembly of the annular disc on the vehicle wheel involves substantial effort and costs.
EP-412 541 shows a disc brake suitable for a high performance brake, with the brake caliper thereof being in the form of a floating frame which is axially guided on a brake carrier integrally connected to the steering knuckle of the automotive vehicle. The brake carrier extends beyond the outer edge of the brake disc. The floating frame encloses four brake shoes disposed on either side of the brake disc and transmits the tensile force. The circumferential forces are transferred from the brake shoes to the brake carrier. The brake carrier, on the axial inner side of the wheel, is connected to the automotive vehicle. In order to enable the circumferential forces of the two axial outer brake shoes to also be absorbed, the brake carrier comprises a carrier arm extending across the outer edge of the brake disc and through the center of the chamber enclosed by the floating frame.
High torque brakes require that the brake shoes have large friction surfaces. Increasing the size of the brake shoes, especially in the circumferential direction of the brake disc, has the disadvantage that the friction surface is no longer has a uniform pressure applied, even if two brake cylinders in side-by-side relationship are used instead of one brake cylinder. Consequently, two short-length brake shoes are used, which are separately pressed onto the brake disc by each of two brake pistons in side-by-side relationship.
An additional requirement placed upon a high performance brake is that its weight should be as low as possible. For increasing the weight of high-torque brakes increases the unsprung weight on the vehicle wheels, which, in turn, has a negative effect on the handling of the automotive vehicle. For this reason, the braking efficiency cannot be enhanced by simply increasing the size of the brake.
It is an object of the invention to improve the brake performance of a disc brake of the afore-described type, while maintaining a low weight.